Agonistic Properties of Cannabidiol at 5-HT1a Receptors

Abstract

Cannabidiol (CBD) is a major, biologically active, but psycho-inactive component of cannabis. In this cell culture-based report, CBD is shown to displace the agonist, [3H]8-OH-DPAT from the cloned human 5-HT1a receptor in a concentration-dependent manner. In contrast, the major psychoactive component of cannabis, tetrahydrocannabinol (THC) does not displace agonist from the receptor in the same micromolar concentration range. In signal transduction studies, CBD acts as an agonist at the human 5-HT1a receptor as demonstrated in two related approaches. First, CBD increases [35S]GTPgammaS binding in this G protein coupled receptor system, as does the known agonist serotonin. Second, in this GPCR system, that is negatively coupled to cAMP production, both CBD and 5-HT decrease cAMP concentration at similar apparent levels of receptor occupancy, based upon displacement data. Preliminary comparative data is also presented from the cloned rat 5-HT2a receptor suggesting that CBD is active, but less so, relative to the human 5-HT1a receptor, in binding analyses. Overall, these studies demonstrate that CBD is a modest affinity agonist at the human 5-HT1a receptor. Additional work is required to compare CBD's potential at other serotonin receptors and in other species. Finally, the results indicate that cannabidiol may have interesting and useful potential beyond the realm of cannabinoid receptors.

Full text

Agonistic Properties of Cannabidiol at 5-HT1a Receptors
Ethan B. Russo,
1
Andrea Burnett,
1
Brian Hall,
1
and Keith K. Parker
1,2
(Accepted June 27, 2005)
Cannabidiol (CBD) is a major, biologically active, but psycho-inactive component of
cannabis. In this cell culture-based report, CBD is shown to displace the agonist, [3H]8-OH-
DPAT from the cloned human 5-HT1a receptor in a concentration-dependent manner. In
contrast, the major psychoactive component of cannabis, tetrahydrocannabinol (THC) does
not displace agonist from the receptor in the same micromolar concentration range. In signal
transduction studies, CBD acts as an agonist at the human 5-HT1a receptor as demonstrated
in two related approaches. First, CBD increases [35S]GTPcS binding in this G protein coupled
receptor system, as does the known agonist serotonin. Second, in this GPCR system, that is
negatively coupled to cAMP production, both CBD and 5-HT decrease cAMP concentration
at similar apparent levels of receptor occupancy, based upon displacement data. Preliminary
comparative data is also presented from the cloned rat 5-HT2a receptor suggesting that CBD
is active, but less so, relative to the human 5-HT1a receptor, in binding analyses. Overall, these
studies demonstrate that CBD is a modest affinity agonist at the human 5-HT1a receptor.
Additional work is required to compare CBD’s potential at other serotonin receptors and in
other species. Finally, the results indicate that cannabidiol may have interesting and useful
potential beyond the realm of cannabinoid receptors.
KEY WORDS: Cannabis; cannabidiol; cAMP; G Proteins; marijuana; serotonin; THC.
INTRODUCTION
Although cannabis and its extracts have been
extensively studied, knowledge of the biochemical
mechanisms of one of its major components, canna-
bidiol (CBD), has not been thoroughly explored (1,2).
This lack of knowledge of CBD’s biochemical phar-
macology is noteworthy in the context of its known
potential in human therapy: for example, it has been
demonstrated to have anxiolytic (3), anti-seizure (4),
anti-psychotic (3), and neuroprotective properties
(5,6). While previously thought to be sedating, recent
clinical research has confirmed that CBD is activat-
ing, and that it counters sedative effects of THC (7).
The major psychoactive component of cannabis,
tetrahydrocannabinol (THC), has received extensive
research attention into its biochemical pharmacology.
Both THC and CBD have been pharmacologically
investigated at cannabinoid receptors (CBR), which
are highly conserved across animal taxa, with the
major exception of insects (8–10). THC is at least 10
times more potent in binding to CB1 receptors than
CB2 receptors. At CB1R, there is evidence to suggest
that CBD is an antagonist or inverse agonist, al-
though substantial debate still exits about its intrinsic
activity (10,11). CBD has received little attention in
other neurotransmitter systems. Noteworthy in this
regard is serotonin (5-hydroxytryptamine; 5-HT),
which is known to be involved in many of the same
processes important to cannabis’s actions (12,13) such
as relief of anxiety, pain, the complex processes of
1
Skaggs School of Pharmacy, The University of Montana,
Missoula, MT 59812-1552, USA.
2
Address reprint requests to: Keith K. Parker, Skaggs School of
Pharmacy, The University of Montana, Missoula, MT 59812-
1552, USA. Tel.: +406-243-4235; Fax: +406-243-5228; E-mail:
keith.parker@umontana.edu
Neurochemical Research, Vol. 30, No. 8, August 2005 (Ó 2005), pp. 1037–1043
DOI: 10.1007/s11064-005-6978-1
1037
0364-3190/05/0800–1037/0 Ó 2005 Springer Science+Business Media, Inc.

headache (14,15), and thermoregulation. The few
studies done with CBD in serotonergic systems
suggest that it inhibits 5-HT re-uptake, and overall
reduces 5-HT neurotransmission (2,16). There is also
some experimental evidence to support CBD’s activity
in other neurotransmitter systems such as dopamine,
GABA, and the endogenous opioid system (2).
Most of 5-HT’s broad actions are thought to be
regulated at a series of 5-HT receptors (5-HTR), the
majority of which (17) are members of the diverse
super family of G-protein coupled (GPC), seven-
transmembrane receptors (7TMR). The 5-HT1aR
(17) has been cloned and studied in numerous in vivo
and cell culture systems and in various species. It has
been cloned in both human (H) and rat (18–20),
amongst other organisms, and has been further
analyzed in other species, including rabbit (21), where
it has not been cloned. In this literature, extending
over two decades, 5-HT1aR has been ever more
implicated in a variety of physiological and
pathological processes including anxiety, mood,
depression, panic, obsessive-compulsive disorders,
headache, immune regulation, and cardiovascular
regulation to name a few (2,6,17,18). Additionally, the
5-HT2aR could have relevance to the pharmacology
of cannabis as it has been associated with phenomena
like mood, headache, and hallucination (22). There is
precedence for the action of cannabinoids such as
oleamide at serotonin receptors (23–26).
Over the last decade our laboratory has con-
ducted a series of studies with 5-HT1aR (27), and to a
lesser extent with 5-HT2aR (21). Because of these
interests and our hypothesis that CBD may have
important actions relevant to the pharmacology of
cannabis but outside the realm of CBR, we report
here studies with H5-HT1aR a nd a limited compar-
ison to the rat 5-HT2aR (28). For both H5-HT1aR
and rat 5-HT2aR we also report comparisons be-
tween CBD and THC. In cell culture experiments
with cloned human 5-HT1aR and rat 5-HT2aR,
CBD has a greater affinity than THC for both
receptors. CBD binds with higher affinity at 5-
HT1aR than at 5-HT2aR. In the case of H5-HT1aR,
CBD appears to act as an agonist. A preliminary
report of these investigations has appeared (29).
EXPERIMENTAL PROCEDURE
Cell Culture. Chinese Hamster Ovary (CHO) cells expressing
the H5-HT1aR (19) were cultured in Ham’s F-12 medium fortified
with 10 % fetal calf serum and 200 ug/ml geneticin. Cultures were
maintained at 37°C in a humidified atmosphere of 5% CO2. Cells
were sub-cultured or assayed upon confluency (5–8 days). Cloned
H5-HT1aR was kindly provided by Dr. John Raymond (Medical
U. of South Carolina). NIH 3T3 cells expressing the rat 5-HT2aR
(28) were cultured under similar conditions in DMEM fortified
with 10% calf serum and 200 lg/ml geneticin. These transfected
cells were generously provided by Dr. David Julius (UCSF). Both
cell lines have been tested for mycoplasma with a PCR kit (ATCC),
and are free of contamination.
Receptor Preparation. Cells were harvested by trypsinization
and centrifuged at low speed in ice-cold medium. The pellet was re-
suspended in ice-cold Earle’s Balanced Salt Solution followed by
centrifugation. Cells were re-suspended in 10 ml of ice-cold binding
buffer (50 mM Tris, 4 mM CaCl2, 10 lM pargyline, pH 7.4),
homogenized with Teflon-glass, and centrifuged for 450,000 g-min.
at 4°C. To produce a crude membrane preparation, the pellet was
re-suspended in 30 ml of ice-cold binding buffer, and homogenized,
first with Teflon-glass and then with a Polytron (setting 4) for 5 s.
The receptor preparation was stored on ice and assayed within the
next 1.5 h.
Assay of Receptor Activity. Binding of the agonist [3H]8-OH-
DPAT ([3H]8-hydroxy-2-(di-n-propylamino)tetralin) to H5-
HT1aR followed well-characterized in vitro protocols (20,27,30).
Radioligands were purchased from New England Nuclear (NEN),
Boston, MA. 1 ml reaction mixtures, in triplicate, were incubated
for 30 min. in a 30°C shaker bath. Composition of the 1 ml reac-
tion mixture was: 700 ll of receptor preparation; 100 ll of either
binding buffer (for total binding) or 10 lM 5-HT (final concen-
tration for non-specific binding), 100 ll of the tritiated agent (final
concentration of 0.5 nM [3H] 8-OH-DPAT), and 100 ll of diluted
CBD or binding buffer in the case of controls.
Reactions were stopped by addition of 4 ml of ice-cold
50 mM Tris buffer, pH 7.4, and subsequent vacuum filtration on
glass fiber filters (Whatman GF/B). Filters were rinsed twice in
5 ml of ice-cold Tris buffer, dried, and counted in 5 ml of Ecoscint
(National Diagnostics) liquid scintillation fluid in a Beckman LS
6500 instrument. Homogenates were assayed for protein to main-
tain a nominal value of 50 lg protein per filter over weekly assays
(31). Total and non-specific binding tubes were run in triplicate.
Assays of the rat 5-HT2aR (28) were conducted under similar
conditions with the 1 ml reaction mixture containing: 700 llof
receptor preparation; 100 ul of either binding buffer (for total
binding) or 10 lM mianserin (final concentration for non-specific
binding); 100 ll of the tritiated agent (final concentration of
0.2 nM [3H] ketanserin); and 100 ll of diluted CBD or binding
buffer in case of controls.
cAMP Assay. CHO cells were cultured to confluency in 12-
or 24-well plates (27). Medium was aspirated and the cells were
rinsed twice in warm, serum-free F-12 medium. Cells were then
incubated for 20 min. at 37°C in 0.5 mls of serum-free F-12 med-
ium containing 100 lM isobutylmethylxanthine (IBMX) and the
following substances (final concentrations) alone or in combination
(see Fig. 3): 30 lM forskolin (FSK; for all treatments); 1 lM5-
HT; 16 lM CBD; and 0.05 lM NAN-190 (NAN). Reactions were
stopped by aspiration of medium and addition of 0.5 ml of
100 mM HCl. After 10 min., well contents were removed and
centrifuged at 4000 rpm. Supernatants were diluted in 100 mM
HCl, and cAMP was quantified (27) directly in a microplate format
by colorimetric enzyme immunoassay (EIA) with a kit from Assay
Designs (Ann Arbor). Triplicate independent samples were assayed
in quadruplicate to increase precision.
[35S]GTPcS Assay. H5-HT1aR membranes from trans-
fected CHO cells were incubated with 5-HT (0.1 lM) and/or CBD
1038 Russo, Burnett, Hall, and Parker

(16 lM); see Fig.2), and the following incubation mixture: 20 mM
HEPES buffer, pH 7.4, 5 mM MgCl2, 1 mM EDTA, 1 mM DTT,
100 mM NaCl, 100 uM GDP, 10 lM pargyline, 0.2 mM ascor-
bate, and 0.1 nM [35S]GTPcS (32). Mixtures were incubated for
30 min. at 30°C, and were terminated by dilution in cold buffer.
The mixture was filtered on GF/C filters, rinsed twice in buffer,
followed by drying and liquid scintillation counting. Negative
control (basal incorporation) was the above mixture minus CBD or
5-HT. Non-specific binding was determined in the presence of cold
GTPcS-(10 lM). Positive control was H5-HT1aR membranes in
the same incubation mixture plus 5-HT. All values reported in
Fig. 2 are for specific binding (total – non-specific) of triplicates.
Dilution of Cannabinoids. CBD and THC were obtained in
dilute (1 mg/ml) solution from Sigma Chemical Co. (St. Louis,
MO). These solutions were stored at 4°C until use and then diluted
in distilled water and finally in the buffer appropriate to the par-
ticular assay. Fresh dilutions of cannabinoids were made daily.
Each final concentration of cannabinoid thus contained some of
the vehicle (methanol). The highest concentration of methanol
encountered in any assay (1%) was then tested in that assay system
for activity. In pair-wise comparative t testing, none of the meth-
anol controls were found to be distinguishable from negative
control (buffer).
Statistical Analysis. All statistics (means, standard devia-
tions, standard errors of the mean (SEM), and t tests) were per-
formed with software provided by Poly Software International; in
some cases, statistics were corroborated by hand using a Hewlett-
Packard Graphing Calculator, HP48. Graphs were constructed
with Excel software provided by Microsoft.
RESULTS
Cannabidiol produces concentration-dependent
displacement of the agonist [3H[8-OH-DPAT from
the H5-HT1aR (Fig. 1). Using crude membrane
preparations from cultured CHO cells transfected
with H5-HT1aR (See methods), CBD diluted in
methanolic buffer displaced agonist by 73 ± 8 %
(S.E.M.) at 16 lM. The highest concentration of
methanol (1%) present at 32 lM CBD produced
only 3 ± 0.5% displacement of agonist, a level
indistinguishable from control when the methanol
and control means are compared statistically. While
CBD was active in the micromolar range, tetrahy-
drocannabinol was unable (108 ± 6% of control) to
produce agonist displacement at a concentration of
32 lM.
The ability of CBD to produce concentration-
dependent displacement of highly potent and specific
agonist from the H5-HT1aR ligand-binding site
raised the question of the intrinsic activity of CBD.
Experiments were designed to test the agonistic
potential of cannabidiol. Since H5-HT1aR is G pro-
tein-coupled, agonist binding would be expected to
increase GTP binding, measurable when the stable
analog of GTP, GTP cS is present in a radiolabeled
form. 0.1 lM 5HT increased [35S]GTPcS incorpora-
tion by 57 ± 7% (Fig. 2) above the basal level (buffer)
in membranes of CHO transfected with the receptor.
Similarly, 16 lM CBD increased [35S]GTPcS incor-
poration by 67 ± 6% above the basal level. Together,
5-HT and CBD increased [35S]GTPcS incorporation
to 123 ± 10% above the basal level, suggesting that
CBD had not reached its maximum possible stimu-
Fig. 1. Displacement of Specifically-Bound [3H]8-OH-DPAT By Cannabidiol (CBD) and Tetrahydrocannabinol (THC) In Membranes
Containing the Human 5-HT1a Receptor. Concentrations are micromolar. Values are the mean ± SEM with n’s=3–6. More detailed
experimental conditions of cell culture, membrane preparation, and drug-receptor binding are outlined in Experimental Procedure.
5-HT1a Receptor Agon ism by Cannabidiol 1039

lation. By reference to CBD’s displacement capacity
at the receptor’s ligand binding site (Fig. 1), 16 lM
CBD occupies about 73% of the available binding
sites.
To further test the hypothesis that CBD is an
agonist at H5-HT1aR, experiments were designed to
measure activity in the adenylyl cyclase (AC) system
negatively coupled to the receptor. In this format, AC
is first stimulated by the natural product forskolin
(FSK) at a concentration of 30 lM (control = 100 ±
5%). 1 lM of the agonist 5-HT reduced FSK -stimu-
lated cAMP to 29 ± 8% of control (Fig. 3). 16 lM
CBD reduced FSK-stimulated cAMP to 38 ± 3% of
control. At a concentration of 0.05 lM, the highly
specific 5-HT1aR antagonist NAN-190 reduced the
5-HT effect to 60 ± 7% of control and the CBD effect
to 76 ± 5% of control, providing further evidence
that CBD is acti ng at the ligand- binding site of H5-
0
50
100
150
200
250
Control 5HT (0.1) CBD (16) 5HT/CBD
% Control (Specific [35S]γ-S-GTP Incorp.)
*
**
Fig. 2. Incorporation of [35S]GTPcS by Cannabidiol (CBD) In Membranes Containing the Human 5-HT1a Receptor. Control represents
incorporation in the basal setting (buffer). Concentrations in micromolar are: 5-HT (0.1); CBD (16). Results are expressed relative to basal
incorporation as mean ± SEM with n’s=9–18. *P<0.01, relative to Control;**P<0.01, relative to 5HT. Further experimental details are
found in Experimental Procedure.
Fig. 3. Inhibition of Forskolin (FSK)-Stimulated cAMP by Cannabidiol (CBD), Serotonin (5-HT), and the inhibitor NAN-190 (NAN) in
Whole Cells Transfected With the Human 5-HT1a Receptor. All conditions contain FSK at 30 lM and the phosphodiesterse inhibitor
isobutylmethylxanthine (IBMX) at 100 lM. Other concentrations in micromolar are: 5-HT (1); CBD (16); and NAN (0.05). Results are
expressed as percentage of FSK control as mean ± SEM with n’s = 3–6. *P<0.05, relative to 5-HT; **P<0.01, relative to CBD. Further
experimental details are found in Experimental Procedure.
1040 Russo, Burnett, Hall, and Parker

HT1aR. At the concentration used here (0.05 lM),
NAN-190 does not reduce FSK-stimulated cAMP
levels on its own (data not shown).
Since the 5-HT2aR is another receptor puta-
tively involved in the pathogenesis of migraine
headache, we conducted a limited comparison at
cloned rat 5-HT2aR. At the highest concentration
of CBD tested (32 lM), 50 ± 5% of [3H]Ketans-
erin is displaced from membrane preparations of
the cloned rat 5-HT2aR. The displacement is con-
centration-dependent as lower concentrations of
CBD progressively displace less ketanserin, until at
8 lM CBD, the effect is barely above control level.
Comparatively, then, CBD is less potent in dis-
placement from the rat 5-HT2aR relative to H5-
HT1aR. As with H5-HT1aR, THC (32 lM) is
inactive in displacement from rat 5-HT2aR. Signal
transduction properties of CBD at rat 5-HT2aR
have not been explored yet.
DISCUSSION
There is substantial literat ure to support the idea
that tetrahydrocannabinol (THC) is responsible for
many of the meaningful and diverse components of
cannabis’ pharmacological activity (33), but other
available evidence supports important contributions
of CBD and other phytocannabinoids and terpenoids
to its pharmacological activity (34,35). It is well
established that the pharmacology of cannabis
combines therapeutic properties (e.g., benefits on
neuropathic pain and spastici ty) (36–39), and lower
urinary tract symptoms (40) that must be weighed
against adverse effects such as intoxication that may
be counter-productive in a therapeutic sense. A
prominent example of the latter is the hallucinogenic
potential of cannabis demonstrated at higher doses,
especially in certain cultural settings. There is also an
outstanding body of experimental evidence to suggest
that THC is hallucinogenic while the closely related
cannabinoid, cannabidiol (CBD) opposes such
activity (3,41).
In pursuit of those pharmacologic al actions of
cannabis that may underlie some of its medicinally
important possibilities, differentiation between TH C
and CBD at the receptor level may be of significance.
This could be especially so at non-cannabinoid
receptors such as 5-HT recept ors. The results shown
in Fig. 1 establish such a contrast in that CBD shows
micromolar affinity in displacing a known agonist,
[3H]8-OH-DPAT, from the 5-HT1aR ligand-binding
site, THC is inactive in the same concentration
range.
CBD’s 5-HT1aR potency could underlie activity
anywhere along the intrinsic activity continuum from
full agonist to silent antagonist. Experiments sum-
marized in Figs. 2 and 3 provide evidence that CBD
is likely to behave a s an agonist in this receptor sys-
tem. Thus, CBD demonstrated the ability to increase
GTP binding to the receptor coupled G protein, Gi,
which is characteristic behaviour of a receptor ago-
nist. These GPCR are further linked to effector signal
transduction sub-systems such as, in the case of a Gi
GPCR, the AC step in cAMP regulation. In Fig. 3,
when AC is stimulated by forskolin (FSK), the ago-
nist 5-HT markedly reduces cAMP production in this
negatively coupled complex. Likewise, CBD acts as
an agonist in these experiments by reducing cAMP
concentration. The results in Figs. 2 and 3 together
support the hypothesis that CBD is an agonist.
Although not completely conclusive in demonstrating
whether CBD is a full or partial agonist, the com-
parable power of CBD and 5-HT at concentrations
that represent less than full receptor occupancy
(Fig. 1) lend support to the full agonist concept.
The contrast between CBD and THC regarding
their interactions at 5-HT1aR relative to CB1R is
striking. THC is at least 10 times more potent in
binding to CB1R; at 5-HT1aR the relationship is just
the opposite, where CBD has micromolar affinity,
and THC shows no binding in the micromo lar range.
At CB1R, THC has sub-micromolar affinity, yet
CBD has micr omolar affinity. The comparison con-
tinues into the realm of signal transduction, where at
CB1R, CBD is putatively an antagonist or inverse
agonist (2); at 5-HT1aR, we have concluded that
CBD is an agonist.
What implications do these results at 5-HT1aR
have for CBD and cannabis? Cannabis is a very
complex mixture of chemical compounds (42), as is
true of most crude natural product drug mixtures.
The dearth of biochemical investigations with non-
psychoactive cannabis components, such as CBD,
create a void of understanding regarding the use of
one or more of these pharmacologically active com-
ponents as therapeutic agents. It has recently been
demonstrated that CBD stimulates TRPV1 (one of
the vanilloid receptors), inhibits the reuptake of
anandamide, and weakly inhibits its hydrolysis (42),
thus making it possibly the first pharmacotherapeutic
agent to modulate endocannabinoid function (1). As
anandamide has already shown activity at 5-HT1aR,
and 36% inhibition of function at 5-HT2aR (14), the
5-HT1a Receptor Agon ism by Cannabidiol 1041

psychopharmacological importance of such relation-
ships is underscored.
The results reported here argue that CBD is active
as an agonist in vitro at H5-HT1a R and that CBD may
also have in vitro actions at the rat 5-HT2aR. Should
CBD prove to have antagonistic activity at 5-HT2A, it
would support its role as a migraine prophylactic agent
(19). Together, these results lend credence to the idea
that CBD and related compounds merit study at a
variety of receptor systems, in a number of species, and
at various levels from the molecular to whole animal.
If, for example, CBD demonstrates clinical activity at
5-HT1aR in vivo, therapeutic possibilities could arise
in a variety of neurological and other physiologically
relevant settings.
ACKNOWLEDGMENTS
The authors would like to thank the following individuals for
their assistance and ideas that contributed to this project: Rustem
Medora, Alicia Christians, Cortney Halley, Sonja Sakaske, Ben
Seaver, and Lynn Parker . The following agencies are gratefully
acknowledged for their financial support of the work: NIH NIG-
MS grants #: GM/OD 54302–01 and 02 and NIH NCRR grant #:
P20 RR 15583 to the NIH COBRE Center for Structural and
Functional Neuroscience.
REFERENCES
1. Russo, E. B. 2003. Introduction: Cannabis: from pariah to
prescription. J. Cann. Therap. 3(3–4):1–29.
2. Pertwee, R. G. 2004. The pharmacology and therapeutic po-
tential of Cannibidiol. Pages 1–52, in DiMarzo, V. (ed.),
Cannabinoids. Kluwer Academic/Plenum Publishers.
3. Zuardi, A. W. and Guimaraes, F. S. 1997. Cannabidiol as an
anxiolytic and antipsychotic. Pages 133–141, in Mathre, M. L.
(ed.), Cannabis in medical practice: a legal, historical and
pharmacological overview of the therapeutic use of marijuana.
NC: McFarland: Jefferson.
4. Carlini, E. A. and Cunha, J. M. 1981. Hypnotic and antiepi-
leptic effects of cannabidiol. J. Clin. Pharmacol. 21(8–9 Sup-
pl):417S–427S.
5. Hampson, A. J., Grimaldi, M., Axelrod, J., and Wink, D.
1998. Cannabidiol, (-)Delta9-tetrahydrocannabinol are neuro-
protective antioxidants. Proc. Natl. Acad. Sci. USA.
95(14):8268–73.
6. Iuvone, T., Esposito, G., Esposito, R., Santamaria, R., Di
Rosa, M., and Izzo, A. A. 2004. Neuroprotective effect of
cannabidiol, a non-psychoactive component from cannabis
sativa, on beta-amyloid-induced toxicity in PC 12 cells. J.
Neurochem. 89:134–141.
7. Nicholson, A. N., Turner, C., Stone, B. M., and Robson, P. J.
2004. Effect of delta-9-tetrahydrocannabinol and cannabidiol
on nocturnal sleep and early-morning behavior in young
adults. J. Clin. Psychopharmacol. 24(3):305–313.
8. McPartland, J., Di Marzo, V., De Petrocellis, L., Mercer, A.,
and Glass, M. 2001. Cannabinoid receptors are absent in in-
sects. J. Comp. Neurol. 436(4):423–9.
9. Pertwee, R.G. 1997. ‘‘Pharmacology of cannabinoid CB1 and
CB2 Receptors’’. Pharmacol. Therap. 74(2):129–180.
10. Thomas, B. F., Gilliam, A. F., Burch, D. F., Roche, M. J., and
Seltzman, H. H. 1998. ‘‘Comparative receptor binding analysis
of cannabinoid agonists and antagonists’’. J. Pharm. Exp.
Therap 285(1):285–292.
11. Petitet, F., Jeantaud, B., Reibaud, M., Imperato, A., and
Dubroeueq, M. C. 1998. ‘‘Complex pharmacology of natural
cannabinoids: Evidence for partial agonist activity at delta 9-
tetrahydrocannabinol and antagonist activity of cannabidiol
on rat brain cannabinoid receptors’’. Life Sci. 63 (1):PL1–PL6.
12. McPartland, J. M. and Russo, E. B. 2001. Cannabis and
Cannabis Extracts: Greater Than the Sum of Their Parts? J.
Cannabis Therap. 1(3–4):103–132.
13. Russo, E. B. 2001. Hemp for headaches: An in-depth historical
and scientific review of cannabis in migraine treatment. J.
Cannabis Therap. 1(2):21–92.
14. Russo, E. B. 2004. Clinical endocannabinoid deficiency
(CECD): Can this concept explain therapeutic benefits of
cannabis in migraine, fibromyalgia, irritable bowel syndrome
and other treatment-resistant conditions? Neuroendocrinol.
Lett. 25(1–2):31–39.
15. Ferrari, M. D. and Saxena, P. R. 1995. 5-HT1 receptors in
migraine pathophysiology and treatment. Eur. J. Neurol.
2:5–21.
16. Hershkowitz, M. 1978. ‘‘The effect of in vivo treatment with (-)
/delta 1-tetrahydrocannabinol, and other psychoactive drugs
on the in vitro uptake of biogenic amines’’. Adv. Biosci.
22–23:351–358.
17. Cowen, P. J. 2000. Psychopharmacology of 5-HT1a receptors.
Nuc. Med. Biol. 27:437–439.
18. Barnes, N. M. and Sharp, T. 1999. A review of central 5-HT
receptors and their function. Neuropharmacol. 38(8):1083–
1152.
19. Fargin, A., Raymond, J. R., Lohse, M. J., Kobilka, B. K.,
Caron, M. G., and Lefkowitz, R. J. 1988. The genomic clone
G-21 which resembles a beta-adrenergic receptor sequence
encodes the 5-HT1a receptor. Nature 335:358–360.
20. Nelson, D. L., Monroe, P. J., Lambert, G., and Yamamura, H.
I. 1987. [3H]Spiroxatrine labels a serotonin 1a-like site in rat
hippocampus’’. Life Sci. 41:1567–1576.
21. Weber, J. T., O’Connor, M.-F., Hayataka, K., Colson, N.,
Medora, R., Russo, E. B., and Parker, K. K. 1997. Activity of
parthenolide at 5HT2a receptors. J. Nat. Prods. 60(6):651–653.
22. Glennon, R. A., Teitler, M., and Sanders-Bush, E. 1992.
Hallucinogens and serotonergic mechanisms. NIDA Res.
Monographs 119:131–135.
23. Hedlund, P. B., Carson, M. J., Sutcliffe, J. G., and Thomas, E.
A. 1999. Allosteric regulation by oleamide of the binding
properties of 5-hydroxytryptamine 7 receptors. Biochem.
Pharmacol. 58:1807–1813.
24. Boger, D. L., Patterson, J. E., and Jin, Q. 1998. Structural
requirements for 5-HT2A and 5-HT1A serotonin receptor
potentiation by the biologically active lipid oleamide. Proc.
Natl. Acad, Sci, USA 95(8):4102–4107.
25. Cheer, J. F., Cadogan, A. K., Marsden, C. A., Fone, K. C.,
and Kendall, D. A. 1999. ‘‘Modification of 5HT2a receptor
1042 Russo, Burnett, Hall, and Parker

mediated behaviour in the rat by oleamide and the role of
cannabinoid receptors’’. Neuropharmacol. 38(4):533–545.
26. Devlin, M. G. and Christopoulos, A. 2002. ‘‘Modulation of
cannabinoid agonist binding by 5-HT in the rat cerebellum’’. J.
Neurochem. 80(6):1095–1102.
27. Ortiz, T. C., Devereaux, M. C., and Parker, K. K. 2000.
Structural variants of a human 5-HT1a receptor intracellular
loop 3 peptide. Pharmacol. 60:195–202.
28. Julius, D., Huang, K. N., Livelli, T. J., Axel, R., and Jessel, T.
M. 1990. The 5HT2 receptor defines a family of structurally
distinct but functionally conserved serotonin receptors’’. Proc.
Natl. Acad. Sci.USA 87:928–932.
29. Hall, B., Burnett, A., Halley, C., Parker, L., Russo, E., and
Parker, K. K. 2004. Pharmacology of cannabidiol at serotonin
receptors. Proc. West. Pharmacol. Soc. 47:43–(M24).
30. Pierce, P. A. and Peroutka, S. J. 1989. Hallucinogenic drug
interactions with neurotransmitter receptor binding sites in
human cortex’’. Psychopharmacol. 97:118–122.
31. Bradford, M. M. 1976. A rapid sensitive method for the
quantitation of microgram quantities of protein utilizing the
principle of protein-dye binding. Anal. Biochem. 72:248–254.
32. Wieland, T. and Jacobs, K. H. 1994. Measurement of receptor-
stimulated guanosine 5’-O-(gamma-thio)triphosphate)binding
by G proteins. Meth. Enzymol. 237:3–27.
33. Wachtel, S. R., ElSohly, M. A., Ross, R. A., Ambre, J., and de
Wit, H. 2002. Comparison of the subjective effects of delta9-
tetrahydrocannabinol and marijuana in humans. Psychophar-
macology 161:331–339.
34. McPartland, J. M. and Russo, E. B. 2001. Cannabis and
cannabis extracts: Greater than the sum of their parts? J. Cann.
Therap. 1(3–4):103–132.
35. Russo, E. B. and McPartland, J. M. 2003. Cannabis is more
than simply Delta(9)-tetrahydrocannabinol. Psychopharma-
cology (Berl.) 165(4):431–2.
36. Berman, J. S., Symonds, C., and Birch, R. 2004. Efficacy of two
cannabis based medicinal extracts for relief of central neuro-
pathic pain from brachial plexus avulsion: results of a ran-
domized controlled trial. Pain 112(3):299–306.
37. Notcutt, W., Price, M., Miller, R., Newport, S., Phillips, C.,
Simmonds, S., and Sansome, C. 2004. Initial experiences with
medicinal extracts of cannabis for chronic pain: results from 34
‘‘N of 1’’ studies. Anaesthesia 59:440–452.
38. Wade, D. T., Makela, P., Robson, P., House, H., and Bat-
eman, C. 2004. Do cannabis-based medicinal extracts have
general or specific effects on symptoms in multiple sclerosis? A
double-blind, randomized, placebo-controlled study on 160
patients. Mult. Scler. 10(4):434–41.
39. Wade, D. T., Robson, P., House, H., Makela, P., and Aram, J.
2003. A preliminary controlled study to determine whether
whole-plant cannabis extracts can improve intractable neuro-
genic symptoms. Clin. Rehabil. 17:18–26.
40. Brady, C. M., DasGupta, R., Dalton, C., Wiseman, O. J.,
Berkley, K. J., and Fowler, C. J. 2004. An open-label pilot
study of cannabis based extracts for bladder dysfunction in
advanced multiple sclerosis. Mult. Scler. 10:425–433.
41. Karniol, I. G., Shirakana, I., Kasinski, N., Pfeferman, A., and
Carlini, E. A. 1974. ‘‘Cannabidiol Interferes With the Effects of
Delta 9-Tetrahydrocannabinol in Man’’. Eur. J. Pharmacol.
28(1):172–177.
42. Bisogno, T., Hanus, L., De Petrocellis, L., Tchilibon, S.,
Ponde, D. E., Brandi, I., Moriello, A. S., Davis, J. B., Mech-
loulam, R., and DiMarzo, V. 2001. Molecular targets for
cannabidiol and its synthetic analogues: effect on vanilloid
VR1 receptors and on the cellular uptake and enzymatic
hydrolysis of anandamide. Br. J. Pharmacol. 134(4):845–852.
43. Howlett, A.C. 2002. ‘‘International union of pharmacology
XXVII classification of cannabinoid receptors’’. Pharmacol.
Rev. 54(2):161–202.
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